The invention presented here relates to a process and device for manufacturing blisters with high barrier properties from a metal-plastic composite foil which can be deep drawn, in particular from an aluminum-plastic composite foil which is held fast in the clamping facility of a device for manufacturing blisters.
The non-uniform stressing of a metal-plastic foil during deep drawing results in the deep drawing ratio in the process as practiced to date being adjusted to accommodate the critical radial region i.e. the ratio is, to disadvantage, reduced.
What is known, for example from the German Pat. No. 2 321 980, is a device for forming cup-like recesses in thin aluminumplastic strip using a shape giving plunger, die and a clamping facility which holds the strip on the die and a thin layer of material of low friction characteristics on the shaping surface of the plunger, the purpose of which is basically to prevent tears forming in the aluminum-plastic composite and to prevent the composite from being subjected to relatively large frictional forces during the deep drawing process. The frictional forces which arise in this process do not, however, depend solely on the layer on the plunger, but also on the coefficients of friction of the metal-plastic foil. When the blisters are to contain foodstuffs or pharmaceuticals, special lubricants are often not permitted on the inside and therefore small changes in the surface of the metal-plastic composite can lead to variable deep drawing behavior or to interruptions in production.
Also known, for example from the German Pat. No. 2 539 354, is a process and device for manufacturing lightweight containers out of a foil of metal, plastic or preferably a metal-plastic composite, whereby the foil is held fast at the edge of an opening and then stretched into the opening to form a cup shape. It is part of the process that the front of the plunger comes to rest in the radial inner region of the freely suspended part of the foil and stretches it to a preform with relatively gently sloping sidewall, and when, by advancing the plunger, one or progressively more shoulders of the plunger come into contact with the sloping sidewall and stretch the preform deeper and wider. With that process the blister is given a stepped sidewall or a very large radius between the sidewall and the base, which is not always desired and often makes it impossible for the blister to take on the particular shape of the contents.
When deep drawing metal-plastic composites, such as for example aluminum-plastic composites by elongation, these materials are particularly highly stressed in the region of the radii or in the zones of the numerous shoulders of the plunger between the base and the sidewall when using the abovementioned process and device. For this reason the deep drawing ratio cannot be increased. It should also be mentioned, in connection with the material of low friction properties in the German Pat. No. 2 321 980, that such a coating suffers to a relatively high degree from wear, and therefore continuous, trouble-free production with such plungers is not possible.
A further disadvantage of the above-mentioned processes and devices for carrying out such processes is that the base of a semi-rigid blister is subjected to no or only partial elongation or pre-stretching in the deep drawing process, and therefore in many cases relatively large basal areas of the blister were up to now only incompletely stretched, and therefore only relatively small deep drawing ratios were reached.
The object of the present invention is to develop a process and device for the manufacture of blisters from a metal-plastic composite which can be deep drawn, in particular from an aluminum-plastic composite by means of which, in particular in the case of relatively large basal areas, a larger deep drawing ratio and therefore larger volume of blister can be achieved than was possible up to now, and as a result of which the disadvantages associated with the above-mentioned processes and devices are avoided.